The invention relates to a mechanism for returning processed work pieces from the output side to the loading side of a processing unit. The mechanism has a transfer mechanism to transfer the work pieces at the output side of the processing unit, a return path for transporting work pieces delivered by the transfer mechanism back to the loading side of the processing unit or to a further processing unit, and a lifting mechanism to lift the work pieces to a return position located above the output position, which is located between the transfer mechanism and the return path and has a lifting platform.
When work pieces, in particular in the form of plates, stripes or ridges are processed, which are in particular made of wood, wood-like or synthetic materials, it is often necessary to perform the processing of a work piece on a processing unit several times. In the present case, a processing unit is mainly understood to represent one or a plurality of processing stations or the so-called continuous-flow-type machines. In these continuous-flow-type machines, different processing operations are performed at one lateral edge each of the work piece during one passage.
Such a processing of the lateral edges of a work piece is, for example, necessary for furniture parts or front parts of kitchen units which have to be processed at all four side edges or the edge areas in order to glue, for example, an edge and process the same. Since these machines have in most cases an oblong form, it is necessary to return the work pieces after one or a plurality of process steps to the loading side.
The simplest possibility to return the work pieces consists in providing one operator each at both ends of the processing unit, one of them inserting die work pieces to the loading side and the other picking up the processed work pieces at the output side of the processing unit and manually returning them one by one or in batches to the loading side. However, such a procedure is very time- and cost-consuming and prevents an optimum exploitation of the processing unit.
For this reason, different return devices have been developed.
According to a known embodiment, the work pieces are placed onto a roller path guided semi-circularly at the end of the processing unit, which turns the work pieces in the horizontal plane by 180xc2x0. The roller path is followed by a return path running in parallel to the processing path and returning back the work pieces to the loading side.
According to German utility model G 200 16 186, instead of the roller path guided semi-circularly, a displacement unit is provided between the processing unit and the return path running beside the processing path: after having been processed in the processing unit, the work pieces are picked up at the output side by driven rollers, and supporting ridges of the displacement unit are passed between these rollers from below to the above lifting the work piece. Thereupon, the supporting ridges are laterally displaced together with the work piece and place the same onto the return path.
Such return devices, in which the return path runs substantially at the same level with the processing path and beside the same, require, on the one hand, a large amount of space alongside the processing machine. On the other hand, the return path becomes very dirty, since finest chips or the like are continuously arising during processing in the wood working industry. Thus, the return path needs a lot of service which is connected with great expenditure.
In order to solve these problems, the return path is arranged above the processing path in the return device according to German utility model G 93 07 220.1, the disclosure of which is herewith completely made subject matter of the present application. The processing path is followed by a transfer mechanism to transfer the work pieces, and a lifting mechanism to lift the work pieces to a return position located above the output level which is located between the transfer mechanism and the return path. The lifting mechanism has a lifting platform which is, for example, vertically adjustable via a lattice grate which is driven through hydraulic or pneumatic cylinders. Here, the return path is preferably inclined between the return position and the loading side such that the processed work pieces are transported back to the loading side by gravity.
This solution has the advantage that the space above the processing device which was not used previously, is now used to return the work pieces. The space required for the return mechanism is greatly reduced and a closely spaced positioning of the processing units in the manufacturing plant is possible. In addition, the return mechanism may directly be attached to already existing processing units. Since the return path runs above the processing path, chips arising during processing will not so easily accumulate on the return path, so that, in addition, the return path will need less service.
If a high throughput is to be achieved during processing, the design of the return mechanism and the required synchronization between processing unit and return mechanism is relatively complicated.
It is therefore the object of the present invention, to improve the known return mechanism comprising return path and lifting mechanism with lifting platform arranged above the processing path such that the cycle performance can be increased without a great deal of controlling and the lifting motion harmonized.
The solution of this technical problem consists in that the lifting mechanism has a crank drive, by means of which the lifting platform can be raised and lowered.
This provides for driving the lifting platform in a simpler manner using a conventional driving motor. The crank drive provides for a conversion of the rotation into a translational motion. Based on this continuous conversion of the rotation into a lifting motion, no complicated electronic equipment for transporting the work pieces is required to synchronize the lifting mechanism with the work pieces coming from the processing unit in order to increase the passage velocity.
Since the lifting movement of the lifting platform is generated by means of the crank drive, a smooth starting of the lifting mechanism is advantageously created preventing thereby that the work pieces, which lie on the lifting platform, are shifted because of their vis inertiae or, even, fall down therefrom. Following this smooth starting, the lifting motion is accelerated and, thus, a high transport velocity of the work pieces is achieved in order to achieve a sufficiently high cycle performance of the return mechanism. Thereupon, at the end of the lifting motion, the speed of work pieces is smoothly reduced by braking in order to safely transfer them to the return mechanism.
Thus, the crank drive assures a smooth starting with a high transport speed followed by a smooth subsequent reduction of speed of the work pieces lying on the platform, without complicated electric, pneumatic or hydraulic controlling being necessary. Hence, a particularly advantageous transport profile is achieved for the work pieces by simple means by the crank drive, with the course of the speed of the work pieces corresponding to the sine or cosine function by the conversion of the rotation into a translational motion.
Advantageous developments of the return mechanism according to the invention are described in the further claims.
According to an advantageous embodiment, the crank drive has a driven rotational axis with a crank being attached thereto. Therein, the lifting mechanism preferably has a travelling rail coupled with the lifting platform, in which the free end of the crank is guided and which is connected with the lifting platform. The lifting motion of the travelling rail is guided by means of at least one guiding rail. Thus, the path of the lifting platform is defined by the guided travelling rail, so that the work pieces are transported via a defined path from the transfer mechanism to a predetermined return position at the return mechanism.
The at least one guiding rail may run vertically or may be inclined relative to the vertical line. According to a particularly advantageous embodiment of the invention, the inclination of the guiding rail is adjustable relative to the vertical line. The adjustment is carried out by means of an actuating device which may be actuated mechanically, electrically, hydraulically or pneumatically. This allows the return mechanism according to the invention to be adaptable to different processing units in that the guiding rail is inclined to such an extent each that the lifting platform may be passed by in front of the processing unit and the return path runs along in front of the existing processing unit.
The travelling rail preferably has hardened ridges to receive the free ends of the crank which are in particular glued-in. By this measure, the abrasion between the moving parts is reduced in order to increase the life of the device. Gluing facilitates the assembly of the ridges into the travelling rail.
The free end of the crank has advantageously a roller which may be moved in the travelling rail in longitudinal direction. By this measure, the abrasion between the end of the crank and the travelling rail is reduced, so that the efficiency of the device is increased.
Rotatable transport rollers are preferably attached to the lifting platform, the rotation axes of which are arranged essentially vertically to the transport direction of the work piece. A work piece which has been transferred from the transfer mechanism to the lifting platform runs on these transport rollers to a suitable position on the lifting platform. The transport rollers may be driven in order to transport the work piece to this suitable position and in particular start the transfer of the work piece from the lifting table to the return mechanism upon completion of the lifting procedure.
In addition, it is advantageous if the crank drive is synchronized with the processing unit, which allows to further increase the cycle performance of the device, since the passage of the work pieces from the processing unit to the transfer unit and, thereupon, to the lifting platform and the return path is coordinated with each other.
The return mechanism preferably has a return path to return the work pieces from the lifting table to the loading side of the processing unit. In a preferred embodiment, the return path is inclined relatively to the horizontal line between the return position and the loading side such that the work pieces are transported back to the processing unit by gravity. In this embodiment, no additional drive is necessary to transport the work pieces back from the lifting platform to the loading side. Here, rotatable transport rollers are preferably attached to the return path, the rotation axes of which are disposed essentially vertically relative to the transport direction of the work piece.
Finally, it is also conceivable to provide the return path with a driven transport path to return the work pieces from the lifting platform to the loading side.